Research On Driving Torque Control System For Electric Vehicle With Four In-wheel BLDC Motors

In recent years, with energy and environment problem becoming increasinglyprominent, the development of new energy vehicles has been the main developmentdirection of vehicle in order to save the energy and protect the environmental. At present, theresearch on the pure electric vehicle become more and more popular in many countries,especially in the developed countries. In-wheel motor drive electric car, because of thein-wheel location of the motor, has a simple structure and high transmission efficiency, easyto realize the control of the driving moment, which has become a hotspot in research ofelectric vehicles.Firstly, as the in-wheel motor is the power source driving the vehicle, research must befocused on the in-wheel motor first of all. Secondly, electric control technology is developedfrom the traditional internal combustion engine vehicle control technology, in order toensure the performance and security of the vehicle, vehicle state information and roadinformation must be attained to formulate the corresponding control strategy. After reviewthe related researches at home and abroad, like vehicle parameters estimation, roadrecognition technology and drive torque control, the research in this thesis aims to estimatethe vehicle speed and road conditions with the help of nonlinear state observer theory andBrush tire model. Meanwhile, design driving moment controller based on the analysis of thesliding mode variable structure control principle to coordinate the torque distribution. Themain researches in the thesis are as follow:1. The advantages and disadvantages of several common motors have been compared,which has demonstrated brushless DC motor is the best choice for the driving motor.According to the structure and working principle of brushless DC motor, built motor modeland its control system model in the MATLAB/Simulink. The model has been proved effective by the test result. Connection has been made between the in-wheel motor and thenonlinear vehicle dynamics simulation in Carsim.2. According to the analysis of several nonlinear system observer development methods,reduced order state observer based on the sliding mode variable structure theory is selectedto estimate the speed of the car. Seven degrees of freedom vehicle model and the UniTiretire model have been built, combine with the existing low cost automotive sensorinformation to estimate the speed of the vehicle with the help of the observer. The result hasbeen demonstrated in Carsim-MATLAB/Simulink union simulation platform.3. In order to provide the optimal slip ratio to drive torque control, brush tire model hasbeen built for the road recognition according to the analysis of the existing road recognition.The longitudinal force reaches the maximum while the vehicle makes full use of theadhesion between road and tire, and the slip ratio is optimal at this time. After estimating theroad‘s maximum adhesion coefficient by appropriate formula based on sliding rate, calculatethe optimal slip ratio while the longitudinal is eighty percent of the biggest. Finally Based onthe Carsim-MATLAB/Simulink simulation platform, the effectiveness of the algorithm hasbeen validated by the different working condition of the vehicle.4. Combine the estimated speed and the identified road information, the sliding modevariable structure controller which has a good error tracking effect has been selected tocontrol the drive torque. The optimal slip ratio is set as the target, adjust the driving torque ofeach wheel in order to use the wheel surface adhesion as much as possible, and then torquecoordination distribution around the wheels and the axles have been analyzed to revealvehicle dynamic performance and meet the stability requirements. Results with and withoutthe driving moment controller have been compared, which proved the applicability and theeffectiveness of the proposed algorithm.